Method of producing steel bars by continuous casting



United States Patent Inventors Fritz Willim Kloten, and Ferdinand Fiala,Thalwil, Switzerland Appl. No. 669,378 Filed Sept. 21, 1967 PatentedOct. 27, 1970 Assignee Concast A G Zurich, Switzerland, a Swiss companyPriority Sept. 23, 1966 Switzerland 13,777/66 METHOD OF PRODUCING STEELBARS BY CONTINUOUS CASTING 17 Claims, 1 Drawing Fig.

[56] References Cited UNITED STATES PATENTS 2,128,941 9/1938 Hudson164/96X 2,840,872 7/1958 Bidner et a1. 164/57 3,182,359 5/1965 Gero164/55X 3,206,808 9/1965 Robinson 164/86 3,421,571 1/1969 Webber et al.164/86 3,421,569 1/1969 Neumann 164/95X FOREIGN PATENTS 1,403,347 5/1965France 164/57 505,427 5/1939 Great Britain 164/82 Primary Examiner.l.Howard F lint,.|r Assistant Examiner-R. Spencer Annear Altome vSandoe,Neill, Schottler and Wikstrom ABSTRACT: A method of producing steelcastings by con- US. Cl .1 164/86, tinuous casting in which at least twoseparate jets of molten 1 steel of different chemical composition arepoured simultane- Int. Cl B22d 11/10 ously into the mold underconditions such that the properties Field ofSeai-ch 164/82. 86, of theperipheral zone of the casting are different from those 7, 231 of thecentral corev I I I6 1 a I I I, {E I v I l t I I 1 1 "T I I 2 j I '5 IO1 7 I r l v I A I I I I 'r-II 1 j s 2 \t m lbw-r5 147: 1/ 4 -;1 1 611p:9 I 9 \g r I e 15 I4 1 i'] METHOD OF PRODUCING STEEL BARS BY CONTINUOUSCASTING The present invention relates to a method of producing steelcastings by continuous casting, wherein liquid molten steel is poured inat least two jets simultaneously into an open-ended chill mould fromwhich the casting formed with a solidified peripheral zone surrounding aliquid core is withdrawn and then guided as well as further cooled in aguide means following the mould.

The quality of the final products obtained from such continuous castingsdepends upon the quality of the surfaces and peripheral zones of thecontinuous castings. A clean surface and peripheral zone without cracksis essential'for further processing, generally in the form of a shapingprocess. Cracks or other surface defects prevent the continuous castingsfrom being satisfactorily processed because the following shapingprocess does not remove them. Such defects are frequently caused by thepresence of nonmetallic exogenic or endogenic occlusions which have notbeen successfully eliminated during the process of producing the steel.Nonmetallic occlusions are primarily deoxidation products, such asaluminum oxide. If these oxides appear in the peripheral zone, they giverise to structural weaknesses which in turn cause the said defects toappear on the surface and in the peripheral zone.

For achieving particular properties the addition of metals for alloyingor improving the steel is often desired. For instance, it isconventional to introduce aluminum into the steel for the purpose ofimproving its resistance to aging, for deoxidising the steel, forrefining its grain and so forth.

However, difficulties arise when it is desired in one casting to combinecertain properties of the peripheral zone with different properties ofthe core. In order to meet such requirements the production of compoundcastings has been developed to permit properties which locally differ tobe imparted to one and the same casting.

It has already been proposed'to produce compound continuous castings bya method in which the solidified casting emerging from one mould isconducted through a second mould in which it forms the core of acompound continuous casting. Another method consists in continuouslycasting a hollow bar which forms a mould for pouring the internal partof the casting into the same. It has also been proposed to producecompound castings by casting the ,core material between metal sheets orplates. However. in all these processes differences in the shrinkagerates and inadequate bonding between the two cast materials createconsiderable difficulties. Moreover. stresses generated during thecasting must be relieved by a thermal treatment.

It is the object of the present invention to produce continuous steelcastings in which the peripheral zones and the cores have differentproperties. by jointly casting steels possessing the different desiredproperties in such a way that an optimum bond will be formed and faultsdue to differential shrinkage avoided.

According to the invention this is achieved by different chemicalcompositions of the steel in the two jets and by the formation of theperipheral zone substantially from the steel of one jet which does notpenetrate deeply into the liquid core but spreads in a substantiallyhorizontal pattern of flow near the bath surface, the formation of saidperipheral zone being assisted by a greater depth of penetration of theother jet into the liquid core in a direction of fiow principallyconfined to the longitudinal axis of the casting.

The proposed method and other features thereof will be more readilyunderstood from the following more detailed description.

Steel is poured in two jets into a chill mould of any desired crosssection, the chemical composition of the steels forming the two jetsbeing different. Should it be desired to cast a slab it is preferred tomake use of three jets, the chemical composition of the steel formingthe two outside jets differing from that of the steel forming the centrejet. Since the depth of penetration of the two outer jets into theliquid core is only,

slight and this steel spreads primarily in the horizontal direction inthe region of the bath surface, the steel from the two outer jetssolidifies principally near the mould wall, so that a peripheral zone ofthe thickness required for further processing is formed substantiallyonly from the steel of these two outerjets.

The formation of this peripheral zone is assisted by imparting to theremaining, i.e. central jet a greater depth of penetration. This canpreferably be done by introducing this jet through an extended pouringspout which dips into the bath to discharge the steel at a point belowthe bath surface in the direction of the longitudinal axis of thecasting. The steel flowing from the two outer jets impedes the flow ofthe steel from the centre jet towards the bath surface and thus preventsthe formation of a solidified shell from the unwanted material. Sincethe two outer jets impinge on the surface of the steel bath in themould, the frequently observed formation of a freezing layer in theregion of the bath surface is obviated by the immersion of the extendedpouring spout.

The extended pouring spout which dips into the bath may have twoadditional lateral outlets from which the steel emerges below the bathsurface parallel to the longer sides of the mould in such a way that itdoes not substantially interfere with the formation of the peripheralzone from the desired steel. Moreover, interference by flowing metalwith the solidification of the surface in the centre region of the widersides of the slab is thus likewise avoided.

The two outer jets may also be confined in and guided by extendedpouring spouts which allow the steel to emerge in a suitable sidewaysdirection for imparting a substantially horizontal direction of flowalong the mould walls to the steel which is intended to form theperipheral zone.

Suitable apparatus for performing the method of this invention isillustrated by the accompanying drawing which is a vertical sectionthrough a mould and through a tundish which has three pouring spouts.

Referring to the drawing. stecl from the tundish 4 is teemed into achill mould 5 through three pouring spouts, a central pouring spout II,and two outer pouring spouts I0 and I2 which are respectively atopposite sides of the central pouring spout II. The tundish is normallyprovided with three plugs 16. one for each pouring spout, for openingand closing the respective spouts.

The three pouring spouts extend below the surface of the bath of steelin the mould, the central spout ll extending deeper than outer spouts l0and 12. The bottom end of the central spout II has a pouring opening 15opening downward for conducting a middle jet 2 of steel down into thesteel in the mould in the direction of the longitudinal (vertical) axisof the mould as indicated.

For producing a killed steel with a content of aluminum, aluminum isintroduced into the middle jet 2 by feeding an aluminum wire 7 into itthrough an opening in the side wall of the central pouring spout.

The outer pouring spouts 10 and 12 each has an outlet 9 in the sidefacing the side wall of the mould and below the surface of the steeltherein, so that the jets l and 3 of steel from the spouts l0 and 12emerge laterally of the mould. The jets l and 3 are thus directedtowards the side wall of the mould 5 at a depth indicated at 8, but theouter pouring nozzles 10 and 12 are spaced and arranged so that the jetsl and 3 entering the bath of steel in the mould do not interfere withthe solidification of the steel in the peripheral zone of the bathindicated at 14.

Different chemical compositions of the steels poured into the mould inthree jets may be provided by subjecting a steel that has been obtainedby any desired method of production to differential metallurgicaltreatments. Such treatments may comprise any method of deoxidation andalloying as well as combinations thereof.

The steel is tapped from a melting vessel into a pouring vessel,preferably a ladle, and then transferred to another pouring vessel, forinstance into the tundish. From this tundish the steel is then teemedinto the mould in three jets.

containing'alumin u'm may also be advantageous.

' the proposed method.

For instance, if it is desired to produce a killed steel withla contentof metallic aluminum, then steel of the same chemical composition may beteemed from the tundish and aluminum simultaneously introduced into themould at a point below the l a 1 bath surface. This aluminum is thenconveniently introduced into the central of the three pouring jets, theterm jet in this context being understood also to includethe jet ofsteel'after its discharge into the liquidcore. The aluminum is uniformlydispersed in the liquid core by' the effect of this jet. The aluminummay be introduced inthe liquid stateorby injecting it monoxide formedduring solidification by the reaction of car-' in granular form belowthe bath surface into the region of flow of the centraljet. However, asa matter, of preference thealu-n minummaybe introduced into the jet inthe form of a .wire

Since for the purpose of obtaining the required penetration in depththis jet is;preferably confined in anextended pouring spout thewire maybe introduced through thewall of this spout. The pouring spoutsimultaneously protects the aluminum'from oxidation. This method hasqualitative and economic advantages because it permitsaluminum to beintrodu'ced into the steel in the desired quantitieswithout theformation of unwanted aluminum oxides by oxidation in contact withatmospheric. oxygen. The quantity of aluminum Another application of;the present inventiori'ariscsin the 'production of deep drawing sheetfrom continuous castings.

, bon and oxygen eseapes from the melt in theforrn of gas bub bies andcausesthe steel to foam over the edge of the mould by the resultantviolent oiling agitationQThis foaming effect, i.e. the intensity of theboiling action. depends inter alia very considerably upon the degree ofdeoxidation of the melt. A

procedure'whieh canbe carriedout within the scope of the required forobtaininga steel having particular properties,

such as resistance toagingyis substantially less thanthat required inconventional processes since nearlythe entire addition vof aluminumremains in}, thesteel in the metallic form.

present invention consists in producing a continuous casting in whichthe peripheral zone and the coreconsist of steels that have beendeoxidised to different degrees. The term degree of.

, :deoxidation isiritended 'to embrace anystatc in the range betweenunkilled and fully killed steel. Within the specified meaning adifference therefore exists for instance between an unkilled, a partlyor a fully killed steel.- i

The difference in the degree of 'deoxidation can be established inapouring vessel by the introduction of deoxi- Moreover, no aluminum oronly a small amount of aluminum,

i and of its oxide reach the peripheral zone. f

An alternative method of producing slabs of killed steel in thisprocedure the steel is tapped from the furnace into a ladle and pouredinto a tundish. This tundish is divided into compartments from which thesteel is poured into the mould in three jets, the two outer. jetshaving-the same composition but differing from that of the central jet.

dants or by some othertreatment, such as a vacuum treatment of thcstccl. From themelting vessel thcisteelmay be tapped into two ladles orintoone divided ladle, the steel in one ladle orinonc compartmentof asingle ladlejbeing submitted to a different treatment to that in theother ladle or ladle compartment. Steels of different chemicalcompositions are then teemed into a divided tundish and thence allowedto run into the mould. Alternatively, steels of different degrees ofdeoxidation may be tapped from two furnaces into two ladies and Thesteel can be transferred in one ladle with two teeming spouts or in twoladies. Moreover, the tundish may be so con structed that the steel canoverflow from one compartment I into the other, in which case'only oneladlewith one teeming spout is required. A portion of or all thealuminum needed for achieving the desired properties may be introducedinto the steel in one compartment of the tundish, preferably in thevicinityof the pouring spout, in such manncrgthat the centre jet of thethree jets from the tundish contains metallic alu-f minum which is thenevenly distributed in the liquidicore of the slab.- However,convenicntly'only. a portion of the aluminum that is to'be added isintroduced into the tundish. the remainder being introduced into thecasting jet that iseonfined inthe extended pouring spout. This procedurehas the j advantage. that the reaction products formed with oxygen canat leastpartly separate in the tundish. If for any reason theintroduction of aluminuminto the centre jet is interrupted, the;

it is naturally possibleito perform any kind of preliminary then pouredinto the mould from the divided tundish. if the employment oftwolatll'cs or of a divided ladle should be impossible. thenthc steel maybe treated in the divided tundish.

A preferred dcoxidant is aluminum, but any desired preliminarydeoxidation may be performed for instance with manhganese. sili'con.vanadium or'with deoxidising alloysindivi'dually or in combination-Another feasible procedure comprises tapping an unkilled steel'into aladle. adding vanadium andadjusting to the final degree of deoxidationrequired either in one compartment of deoxidation in the furnace or inthe ladle in conjunction with ilt is well known-that killed steelsoftenhave surface faults,

" known as pinholing' which do notclose and fuse together during thefurther processing, and which therefore lead to unacceptable fnalproducts. it has been established that an the peripheral zone of thecasting.

In the production of alloyed steels the alloying elements may be addedin the furnace or, if the additions are small, they may be introducedinto the ladle, as is conventional. By using two pouring vesselscontaining differently alloyed steels ir the 7 method according to theinvention, castings can be produced which consist of differently alloyedsteels in their cores and surface zones.

thedividcd tundish or in theextended pouring spout of the central jet.steels of different degrees of deoxidation being pourcdinto thc mould.

I Formany applications the material should be resistant to aging; Sincealuminum inactivates the. nitrogen in the steel vwhich causes aging bybinding the same as a nitride, steels that have been fully killed withaluminum are. also largely resistant to aging provided the addition ofaluminum is adequate to bind the nitrogen besides the oxygen."

A very useful method of performing the present invention consists incombining the properties of unkilled steel with the properties of akilled steel'in one and the same cast product.

For the production of slabs for making deep drawing sheet that isresistant to aging an unkilled steel ispreferably used for forming theperipheral zone and a killed. steel for forming the corel'The advantagesafforded bytheinvention consist in that the unkilled steel solidifies ina peripheral zone which has a clean surface favourable forfurther-processing and thatthe undesirable foaming which occurs when an.unkilled steel is cast does not occur because the aluminum-enrichedcores of fully killed steel at least substantially prevents thegeneration of CO bubbles in the transitional region to the peripheralzone that has been formed. e

. Moreover, it is also desirable to avoid the undesirable both, therebyto produce a steel in the core that has been fully killed with aluminumand that is also resistant to aging. The quantity of aluminum thatshould be added may amount to but not exceed about 800 g/ton of steel.This is far less than the quantity normally needed. However, forachieving resistance to aging other elements capable of binding nitrogenmay likewise be used. such as vanadium alone or incombination with thealuminum.

The quality of the casting and final product depends not exclusivelyupon the purity of the surface and of the peripheral subsurface zone,but also upon the thickness of this latter zone. For a given set ofcasting parameters this thickness can be controlled by adjusting therelative proportion of the steel poured in the two outer jets to thesteel poured in the centre jet as well as by appropriately adjusting thedepth of immersion of the extended pouring spout in the bath, i.e. thedepth below the bath surface at which the jet forming the core actuallyemerges.

When casting is to begin the mould is preferably first filled with thesteel that is to form the peripheral zone, the steel that is to form thecore not being poured until the process of withdrawal begins.

In the majority of applications of the proposed method the use of a'plugor the like for controlling the volumes of steel that are to be pouredis advisable.

During the process of continuous casting it is impossible to preventfluctuations in the withdrawal rate due to technical causes. These mustbe compensated by suitably controlling the rate of pouring the steelinto the mould. In order to ensure that the quality of the casting isuniform it is advisable to regulate the quantity of aluminum that isintroduced by reference to the rate of withdrawal of the casting.

The above mentioned examples do not exhaust the possibilities that areinherent in the invention. For instance, it may also be desired toimpart particular properties to the peripheral zone by alloying specificelements with the steel for forming this zone.

We claim:

1. A method of producing a compound casting having a peripheral zone anda core, composed of steel having respectively different properties, bycontinuous casting wherein liquid steel is poured in one end of anopen-ended chill mould that solidifies a peripheral zone of steelsurrounding a liquid core to form a casting which is withdrawn from theother end of the mould and thereafter further cooled, said methodcomprising simultaneously pouring into the mould by separate jets ofliquid steel of respectively different chemical composition forsupplying steel of different chemical composition respectively to theperipheral portion of the mould and to the core portion, thereby to forma steel casting having a peripheral zone and a core of respectivelydifferent chemical composition, a jet of steel for forming the corebeing directed to penetrate more deeply into the liquid in the mould inthe direction of the longitudinal axis of the casting than a jet ofsteel for the peripheral zone, said jet for the peripheral zone beingdirected to spread in a substantially horizontal pattern of flow nearthe free surface of liquid steel in the mould.

2. The method of claim 1 in which the pouring of metal into the mouldfor the peripheral zone is begun before starting withdrawal of a castingfrom the mould, and the pouring of metal for the core is begun afterwithdrawal of said casting is started.

3. The method of claim l in which the relative amounts of metal pouredinto the mould by the respective jets for the core and peripheral zoneare varied for adjusting the relative thickness of the peripheral zone.

4. The method of claim 1 in which ajet of metal for the core isconducted and discharged into metal in the mould below the surface ofsaid metal.

5. The method of claim 4 in which the relative amounts of metal pouredinto the mould by the respective jets for the core and peripheral zoneand the depth below the surface of metal in the mould at which metal forthe core is discharged, are

varied for adjusting the relative thickness of the peripheral zone.

6v The method of claim 1 in which at least one of said jets impinges onthe surface of metal in the mould.

7. The method of claim 1 in which said jets are each conducted anddischarged into metal in the mould, below the surface of said metal, ajet of metal for the peripheral zone being directed to flow along a wallof the mould in the region of the surface of said metal.

8. The method of claim I wherein said mould has a lateral elongatedcross section for easing a slab in which metal is poured into the mouldin three jets, there being two jets of metal for the peripheral zone andone of metal for the core, said jet of metal for the core beingdischarged into metal in the mould below the surface of said metal, andsaid jets of metal for the peripheral zone being directed to penetratebelow the surface of metal in the mould less than the jet of metal forthe core.

9. The method of claim 1 wherein said mould has a laterally extendedcross section ofcasting a slab, in which ajet of metal for the core isdischarged into metal in the mould, below the surface of said metal. inthe direction of the elongated dimension ofthe mould.

10. The method ofclaim 9 in which metal is poured into the mould inthree jets. there being two jets of metal for the peripheral zone andone of metal for the core. the two jets of metal for the peripheral zoneeach being conducted and discharged into metal in the mould, below thesurface thereof, and each being directed for the metal for theperipheral who to flow along walls of the mould.

11. The method of claim 1 in which said separate jets are jets of metalhaving different properties respectively.

12. The method of claim I in which each of the jets are jets of the samemetal and a different metal to commingle with the metal of one of thejets is introduced therein.

13. The method of claim 12 in which said different metal is introducedin powder form.

14. The method of claim 1 in which a wire of a metal is introduced intothe jet of metal for the core.

15. The method ofclaim l in which each of the jets ofmetal are jets ofliquid steel, and in which aluminum is introduced into the jet of metalfor the core below the surface of metal in the mould.

16. The method of claim 15 in which the aluminum is in granular form.

17. The method of claim 15 in which the aluminum is in the form ofawire.

